That painful feeling you get in your ass muscles when sitting for a very long time. Usually the result of long gaming sessions or Harry Potter films.

Cam: "I'm not gonna be able to sit down tomorrow, dude"
Matt: "Why not?"
Cam: "Transformers 3 gave me the worst theater ass. I'm gonna have to get my mom to rub Bengay on it before bed."
Matt: "Oh iite"